> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getsly.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Sign a voucher

> Sign a voucher for a unit of service. Budget decrements; remaining balance returned in response.



## OpenAPI

````yaml /api-reference/openapi.json post /v1/mpp/sessions/{sessionId}/voucher
openapi: 3.1.0
info:
  title: Sly API
  description: >-
    The Agentic Economy Platform — stablecoin payments, agent wallets,
    multi-protocol commerce, and AI agent orchestration.
  version: 1.0.0
  contact:
    name: Sly
    url: https://getsly.ai
    email: support@getsly.ai
servers:
  - url: https://api.getsly.ai/v1
    description: Production
  - url: https://sandbox.getsly.ai/v1
    description: Sandbox
security:
  - bearerAuth: []
paths:
  /v1/mpp/sessions/{sessionId}/voucher:
    post:
      tags:
        - MPP
      summary: Sign a voucher
      description: >-
        Sign a voucher for a unit of service. Budget decrements; remaining
        balance returned in response.
      parameters:
        - schema:
            type: string
          required: true
          name: sessionId
          in: path
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              properties:
                amount:
                  type: number
                  exclusiveMinimum: 0
                description:
                  type: string
                request_id:
                  type: string
              required:
                - amount
      responses:
        '201':
          description: Voucher signed
          content:
            application/json:
              schema:
                type: object
                properties:
                  data:
                    $ref: '#/components/schemas/MPPVoucher'
                  budget_remaining:
                    type: string
                required:
                  - data
                  - budget_remaining
        '402':
          description: Insufficient session balance
          content:
            application/json:
              schema:
                allOf:
                  - $ref: '#/components/schemas/Error'
                  - properties:
                      error:
                        type: string
                      code:
                        type: string
                      details: {}
        '409':
          description: Session closed / exhausted
          content:
            application/json:
              schema:
                allOf:
                  - $ref: '#/components/schemas/Error'
                  - properties:
                      error:
                        type: string
                      code:
                        type: string
                      details: {}
      security:
        - bearerAuth: []
components:
  schemas:
    MPPVoucher:
      type: object
      properties:
        id:
          type: string
        session_id:
          type: string
        amount:
          type: string
        description:
          type:
            - string
            - 'null'
        request_id:
          type:
            - string
            - 'null'
        signed_voucher:
          type: string
          description: Signed voucher the service verifies to collect payment
        created_at:
          type: string
          format: date-time
      required:
        - id
        - session_id
        - amount
        - signed_voucher
        - created_at
    Error:
      type: object
      properties:
        error:
          type: string
        code:
          type: string
        details: {}
        request_id:
          type: string
      required:
        - error
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: >-
        API key (pk_test_* or pk_live_*), JWT session, agent token (agent_*),
        Ed25519 session (sess_*), or portal token (portal_*).

````